PROJECT SUMMARY/ABSTRACT Controlling cariogenic biofilms is the key for prevention of dental caries. However, it is a significant challenge to disrupt robust extracellular polymeric substances (EPS) matrix structures or kill embedded bacteria. Therapeutic treatments using chemical or physical means inadequately control cariogenic biofilms and fail to reduce caries risk. To address this problem, we propose a completely novel removal strategy by transforming biofilms from sticky into brittle, not dependent on enzymatic or chemical degradation of EPS. We have designed a low molecular weight cationic methacrylate polymer that can penetrate into a biofilm matrix and bind to the anionic biofilm biopolymers by electrostatic interactions. This action can crosslink the biofilm matrix, preventing structural re-arrangement of the EPS matrix under stress, and thus it causes cohesive failure and untimely biofilm removal. Strikingly, our study demonstrated that the polymer removed 60% of Streptococcus mutans biofilm biomass by using hydrodynamic cycles for 30 sec, while chlorhexidine and cationic surfactant (CTAB) failed to remove the same biofilms. In this study, we will extend our approach to address the unmet challenge of targeting cariogenic biofilms. We hypothesize that pH-responsive smart polymers can be designed to switch from neutral to cationic states by acidic pH, and thus their anti-biofilm and bactericidal activities can be triggered only in the acidic microenvironment of cariogenic biofilms, but not in neutral healthy biofilms. To test this hypothesis, we will design and develop a random copolymer with an equal number of cationic ammonium and anionic carboxylic groups, that switches from neutral charge to cationic at the pH of 4.5 due to the protonation of carboxylic groups. The significance of this study is to design and develop a highly effective, safe, and straightforward anti-biofilm approach, as compared to current inadequate treatments using chemical and biological agents. The innovation of this study is the combination of mechanisms that target the inherent physicochemical (acidic microenvironment) and mechanical (viscoelasticity) properties of a biofilm matrix to achieve selective and effective removal of cariogenic biofilms. In Aim 1, we will evaluate the acid- triggered bactericidal activity of copolymer against planktonic oral bacteria. In Aim 2, we will evaluate its efficacy and selectivity to remove acidogenic biofilms and kill embedded bacteria by using saliva-derived biofilm models. The proposed approach has the significant potential of reducing the risk of disease for individuals at risk of tooth decay improving the lives of millions of people.